1. Field of Invention
The present invention relates to a display panel. More particularly, the present invention relates to an optical interference display panel.
2. Description of Related Art
Due to being lightweight and small in size, a display panel is favorable in the market of portable displays and other displays with space limitations. To date, in addition to liquid crystal display (LCD), organic light emitting diode (OLED) and plasma display panel (PDP) modules, a module of the optical interference display has been investigated.
U.S. Pat. No. 5,835,255 discloses a modulator array, that is, a color-changeable pixel for visible light which can be used in a display panel. FIG. 1A illustrates a cross-sectional view of a prior art modulator. Every modulator 100 comprises two walls, 102 and 104. These two walls are supported by posts 106, thus forming a cavity 108. The distance between these two walls, the depth of cavity 108, is D. The wall 102 is a light-incident electrode which, according to an absorption factor, absorbs visible light partially. The wall 104 is a light-reflection electrode that is flexed when a voltage is applied to it.
When the incident light shines through the wall 102 and arrives at the cavity 108, only the visible light with wavelengths corresponding to the formula 1.1 is reflected back, that is,2D=Nλ  (1.1)
wherein N is a natural number.
When the depth of the cavity 108, D, equals one certain wavelength λ1 of the incident light multiplied by any natural number, N, a constructive interference is produced, and a light with the wavelength λ1 is reflected back. Thus, an observer viewing the panel from the direction of the incident light will observe light with the certain wavelength λ1 reflected back at him. The modulator 100 here is in an “open” state.
FIG. 1B illustrates a cross-sectional view of the modulator 100 in FIG. 1A after a voltage is applied to it. Under the applied voltage, the wall 104 is flexed by electrostatic attraction toward the wall 102. At this moment, the distance between the walls 102 and 104, the depth of cavity 108, becomes d and may equal zero.
The D in the formula 1.1 is hence replaced with d, and only the visible light with another certain wavelength λ2 satisfying the formula 1.1 produces constructive interference in the cavity 108 and reflects back through the wall 102. However, in the modulator 100, the wall 102 is designed to have a high absorption rate for the light with the wavelength λ2. Thus, the incident visible light with the wavelength λ2 is absorbed, and the light with other wavelengths has destructive interference. All light is thereby filtered, and the observer is unable to see any reflected visible light when the wall 104 is flexed. The modulator 100 is now in a “closed” state.
As described above, under the applied voltage, the wall 104 is flexed by electrostatic attraction toward the wall 102 such that the modulator 100 is switched from the “open” state to the “closed” state. When the modulator 100 is switched from the “closed” state to the “open” state, the voltage for flexing the wall 104 is removed, and the wall 104 elastically returns to the original state, i.e. the “open” state, as illustrated in FIG. 1A.
However, the light-reflection electrode (the wall 104) is a membrane, typically made of metal, and generally is manufactured with a “sacrificial layer” technique widely used in the production of micro electro mechanical systems (MEMS). The light-reflection electrode is very thin and is easily damaged by even a tiny external force, inhibiting it from functioning properly. Moreover, the cavity 108 that spaces the two walls 102 and 104 is hollow. In practice, an external environment usually affects and lowers the display performance of the color-changeable pixel 100 because of the thin cavity 108.
For example, water in the air tends to adsorb into the cavity 108. The depth D of the cavity is typically less than 1 μm, and therefore the adsorbed water generates an undesirable electrostatic attraction between the two electrodes. When the color-changeable pixel 100 is supposed to be in the “open” state, the electrostatic attraction created by the adsorbed water causes the two walls to be attracted to each other, making the color-changeable pixel 100 appear to be in a “closed” state. The light-reflection electrode can also be hindered from normal switching by dust from the air which can enter into the cavity 108. Additionally, the two thin walls 102 and 104 are easily oxidized by air to such an extent that their optical or electrical properties are adversely affected.